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Practical Considerations for Dyno Calibration

During testing we found these vehicles heat soak VERY quickly on a dyno.  Even with a dyno cell with a proper ventilation system we found it simply did not recreate the kind of air cooling created by the car actually moving and as a result the cooling system was overtasked.  Once we realized this we began to tune the car in 4-5 pull increments followed by a waiting period  (sometimes as much as 6 hours on the 100 degree days we get here) before tuning again.  Understanding this was a serious impediment to calibration efforts we endeavored to create a better cooling solution.  Depending on your setup and the number of these vehicles you plan to tune, it's a good idea to improve your cooling options or set your customer's expectations accordingly.

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Custom Cooling Solution

Factory Calibrations

The 4.0l Horizontally opposed 6-cylinder engines are identical across the products despite the fact that the Spyder and GT4 versions are rated at higher horsepower from the factory.

Given the exact same motor is used in all 718 4.0l vehicles, we were suspicious of how Porsche made an additional 20HP in the two models.  The extra power is entirely in the calibration, and simply making the same changes to the GTS model will bring it up to the same power level of the other two.

From testing on the dyno we found the power curves stock to be fairly similar at lower RPM.  At higher RPM where the Spyder/GT4 start to pick up additional power you'll see the GTS begin to fall off.  This is partially attributed to the lower RPM limit, but additionally we found the stock GTS calibration limits throttle opening at higher RPM, those simple changes account for the entirety of the power difference between the two vehicles.

Looking at the chart below you can see that the power curves of the stock values are fairly similar until the GTS vehicles fall off towards the top. Once tuned the vehicles make what is essentially identical power.

The ECU as a System

Porsche calibrations, regardless of ECU variants will require torque limits and targets to be adjusted (typically raised) to meat your goals.  At the end of the day being able to adjust those tables and have everything work in concert is your goal.  Within the range of Porsche vehicles there are a variety of tuning strategies which make achieving this goal a different process.  This tends to mean that if you are an expert with 991.2 turbo 911 cars, everything will look somewhat familiar, but you'll still face a small learning curve in terms of exactly which tables require changing.

These ECUs have very well modeled tables looking for a fairly consistent level of vehicle operation.  This means that in order to produce a finished calibration, you'll need to make a large range of changes.  It's not possible to only change one parameter at a time and expect to make sustainable power.  As an example, if you are working to optimize factory ignition timing or fuel, you will not see an increase of power in the presence of the factory torque limits and targets.  In order to make power and tune the car the best way to start is to push the limits out of the way (but to a safe limit) in order to keep the vehicles behavior and targets consistent with the power you're targeting for your powertrain and fuel.

In order to preserve the balance of driveability and speed that the factory clearly worked so hard to achieve, it's recommended to minimize the table changes you do make.  This seems counter intuitive when we just told you that you need to adjust more tables than you think, but if there is a change you feel may not be important or related to the desired behavior of the vehicle we recommend returning it to stock.  This makes sure that the character of the vehicle can be preserved, and any undesireable effects from the complex interrelation between tables doesn't cause any issues.

COBB OTS Mapping Changes Explained

Torque Targets

Driver Torque Demand (Accelerator Pedal and Clutch)

There are several tables within the Torque Control folder that control and describe the relationship between the accelerator pedal position and the torque the engine gives in response.  Because the Accelerator pedal acts as a torque selector for the driver and is one of the few ways the driver communicates with the engine, it can have a huge impact on the driveability/character of the vehicle.  Do you want a car that with the slightest input takes off?  Or do you want a mild mannered daily driver that can but the hurt on that prius in the next lane?

These tables all function primarily as a torque request, however if they aren't raised high enough to hit the torque the vehicle is producting, it can also functionally act as a limit on the torque requests.  This is because if your torque request maxes out at 400, but your car thinks it can hit 500, it will see that you're only asking for 400 and respond accordingly.

In our calibrations we raised the higher demand sections (higher Rpm/Accelerator pedal %) to a higher torque request in order to hit the increased power we were targeting.  In order to maintain driveability we left the lower sections stock.

In areas of RPM / pedal position the vehicle will find itself sitting in or transitioning through frequently (cruise/around town part throttle driving) it's a good idea to make sure there are no abrupt transitions, as that can lead to the feeling of surging or disproportional acceleration while trying to maintain a consistent speed.

Torque Limits

The factory ECU is constantly calculating torque output in order to deliver exactly the output that Porsche designated by using a variety of torque limits.  The purpose behind that is in order to create a calibration that performs the same in all conditions.  This means regardless of temperature, ambient pressure or other variables it would go after the same amount of power.  Our goal is to remove or adjsut these limits in order to produce our new higher power output.

Within the Torque Control folder all of the tables that list Maximum Available Torque in their name function as limits.  We found that in order to make additional power on all three vehicles we needed to raise all of these tables to their maximum values and utilise other functions such as torque requests to limit the torque created. Because these no longer function as limiters we needed to find other ways to do so.

A second option in order to remove the torque limits are  additional tables called the Engine Speed Threshold for Valid Actual Engine Torque.  Functionally these tables set the timer for how frequently the ECU looks at the torque output.  In effect by increasing the timer delays and adjusting the RPM activation points you can choose when (if at all) the computer is actually referencing the torque limits in some caess entirely removing them from being processed as pat of the torque control strategy.

How you choose to use these tables is up to you and the goals for your calibration.

Load Control

For this collection of vehicles, adjusting the relative load request and limits is the easiest way to get them to target additional airfow and boost and thus achieve a higher amount of torque.

Within the Load Tables folder there are several tables that describe the Maximum Load.  These tables function as targets and limits.  Relative load becomesthe cylinder fill target.  The cylinder fill target then creates the airflow request which is translated into boost request and torque.  If your cylinder filling, boost, and torque limits are all set accordingly, adjusting these tables will allow you to make additional load and power.

One thing that can get confusing is that some phrases are used interchangeably in the operation of the ECU (from the factory)

Relative Load % and Cylinder Filling

Torque Percentage and Relative Load

Maximum Cylinder Filing (A limiter) Is defined by the Relative VE of the Combustion Chamber.  This table is defined as a function of RPM and makes it very easy to see the relationship of cylinder filling to torque as the values look identical when compared to the torque curve of the vehicle on a dyno graph.  

Relative Load And Cylinder Filling

The relationship of load and cylinder fill is fairly similar to the relationship between torque and airflow on the other porsche platforms as well as VW and Audi vehicles.  In this case the Maximum Relative Load table references the Optimum Engine Torque table in order to determine a Target Filling

The other way that Porsche described the relationship between Relative Load% (Cylinder Filling/Airflow) is in the Optimum Torque for Monitoring Engine Function table.  There may be one or more of these tables depending on the rom.  This table is the same data as the Optimum Engine Torque table above, but the Z Axis (Relative Load%) is now the Y- Axis and Relative Load is now the Z Data.  Just like with the Torque and airflow tables on other vehicles, if you change one of these tables you will need to change them both in order to ensure proper function.

Why Change the Relationship Between Cylinder FIll and Relative Load?  In some cases it might be desireable to increase the cylinder fill for the given load.  This will increase power, however any deviation from factory load calculations will impact the way the vehicle drives both in engine response and transmission shifting.

Load Limiters

Within the Limiters folder there are a series of tables that describe Influence of Intake Temperature on Maximum Filling

These tables (quite logically) adjust Relative Load % (Cylinder Filling) as intake air temperatures rise.  While they can be adjusted to reduce the reduction and keep the car producing the same into hotter conditions, keep in mind that these tables are in place to ensure stable and safe driving operation so while some change is going to be fine, there will be a point where you will potentially be compromising the size of the safety margin the vehicle is operating with.

Ignition Timing

The Ignition Timing on these vehicles is similar to may other VAG products in that it has a The stock ignition timing system works very well in response of meeting the needs of both stock operation and the increased load targets you'll typically see with tuning.  Given that this vehicle is designed to run from the factory on 93 octane it was unsurprising that we did notice some knock response under heavy load when using 91 octane fuel.  As a result timing was reduced in order to create a calibration more suitable for that fuel while still having a performance improvement.  On the opposite end of the spectrum we found that adding some timing when the fuel allowed it we were able to pick up some power, particularly on 100 octane fuels.

The main ignition tables you'll need to modify are

• Ignition Timing (Normal) 1

• Ignition Timing (Normal) 2

• Timing Map

• Timing Map Variant 2

These establish the timing under most normal driving conditions based on load and RPM.  While the values in these tables aren't fully identical it's best practice to offset the tables by the same amount when making changes.  I.E. Remove/Add 1.5 degrees from the same point of the table.

It's very easy to see the output of the engine match the shape of the timing, so while the tables aren't identical, it's good to try and match the shape of the ignition curve between each of the tables.

Delta Timing from Continuous Knock

The newer operating systems used in Macan and 4.0L NA Porsche applications have a new monitoring system labeled as Delta Timing from Continuous Knocking (DTCK). This table in the software acts similar to the DAM system in subaru, as it is actively adjusting the allowed ignition timing based on a learned knock response (Knock observed over time).  While thhis table is able to be modified, we recommend leaving it stock as it is a clear safety system for the car that operates properly, and shouldn't impact the ability to tune the vehicle provided the ignition timing values you target don't cause knock.

The monitor for DTCK is actually reporting the potential timing reduction that can be applied in the event that continuous knocking is recorded.  It is NOT a measure of timing actively being removed.  If you refer to the final ignition timing of any given cylinder in a datalog, you’ll see that it does not incorporate the output value from DTCK.

Fuel System

These vehicles do not have a fuel table for full load.  The only fuel control available is related to EGT control and component protection.  So for the most part, under all conditions the cars target a Lambda of 1 (14.7:1), the only thimes there are changes to the AFR is when the vehicle goes into component protection as an effort to control EGT and protect components of the engine.  This richer target will cause a cooling effect serving to protect the exhaust components and (in many cases) produces more torque.  So you'll see the car typically running lean on the street (and hypothetically as clean as possible) as soon as you drive the car hard (on the track etc.) it begins to change to target the richer fuel targets.  

In our experience, the stock fuel tables and control systems with some small tweaks were perfectly sufficient to make extra power and torque needed for our OTS maps.  Our strategy caused the vehicle to enter component protection mode earlier during high load use of the vehicle.  This ensures exhaust components are protected earlier, and it limits the extremely rich mixtures used by the stock strategy to "rescue" components.

We found that the extra fuel molecules present at ~12/13:1 ratio will begin to make more power.  You acn see this represented on the lambda efficiency torque characteristic.  It attempts to make the most torque at 

In a nutshell we are going into component protection earlier, and causing component protection to target a leaner mixture (rather than the extremely rich ones used by the factory) to result in additional power, and a generally leaner overall high load enrichment targetto Furthermore, using stock almost completely stock calibration strategy for low and medium load means that Porsche’s strategy to produce an emissions appropriate vehicle is preserved.  Your end goal should be to get the vehicle appropriately rich for power while keeping it clean and efficient during normal load driving and avoiding some of the significantly over rich AFR values found in the normal component protection tables.  For those wishing to push these vehicles further you may need to take additional steps.

Throttle Control

Earlier in the tuning guide we introduced the idea that Porsche had limited the power of the GTS compared to the mechanically identical motor in the GT4/Spyder. We discovered there are a series of tables that limit throttle opening angle as a means of limiting GTS power.  It's a quick power gain if you simply go through and increase the throttle target limit to allow the vehicle to always have full throttle.  For the affected cars, the table Throttle Target Limit is one of the main ones to look at, this table is not present on the GT4.  As you can see from the table below, it progressively disallows throttle everywhere above 6000rpm.